In a case of rolling a steel sheet by using rolling stands each having a pair of rolling mills, the steel sheet may sometimes “meander”; that is, conveying positions of the steel sheet may vary in the width direction of the rolling mills. Since side guides that guide the width-directional position of the steel sheet are disposed on the entering side of each of the rolling stands, a largely meandering steel sheet has contacted with either of the side guides in some cases.
In a case where the steel sheet contacts with either of the side guides, a fractured piece of the steel sheet may scatter and be pressed into the steel sheet, which may form a defective steel sheet. Further, in a case where the fractured piece pressed into the rolling mill generates a scratch on the surface of the mill, the scratch on the mill will probably be transferred on a steel sheet that is rolled. In this case, the rolling mill needs to be replaced with a new one, failing to execute an efficient rolling process.
Accordingly, Patent Documents 1 and 2 as the related art, for example, propose methods of measuring and controlling the meandering of the steel sheet. Patent Document 1 proposes a method of detecting the meandering on the basis of a deviation of a rolling load in the width direction of the rolling stand so as to adjust the roll gap, for example. Patent Document 2 proposes a method of measuring the meandering amount of the steel sheet by imaging, with an imaging unit, a steel sheet that is conveyed between rolling stands in a final rolling apparatus of a hot-rolled steel sheet, the apparatus including a plurality of rolling stands that are lined up in the rolling direction.